It is often desirable when operating two motors simultaneously to provide for the automatic activation (or deactivation) of one of the motors, referred to as the secondary load, in response to the activation (or deactivation) of the other motor, referred to as the primary load. For example, operation of a vacuum cleaner motor (hereinafter "vacuum motor") has been conditioned upon the operation of a power tool. In this way, the vacuum motor may be automatically activated to collect particulate matter generated by the power tool. Such conditioned operation has been provided by a control circuit that generally includes a current sensor to detect current flowing to the power tool (see, e.g., Samann U.S. Pat. No. 5,120,983). The current sensor, in turn, drives a triac or other switching element disposed between the power supply and the vacuum motor to permit current flow thereto.
It is also desirable to operate the vacuum motor independently of the power tool. Accordingly, such control circuits have included a three-position switch to determine whether the vacuum motor is to be inactive ("OFF"), operated independently from the power tool ("ON"), or activated in coordination with the power tool ("AUTO"). See Robitaille et al. U.S. Pat. No. 5,747,973. However, having to toggle between the three switch positions may be both inconvenient and confusing for a user of the vacuum cleaner.